United States calculator
Calculate z-scores and normal-curve probabilities
Enter a mean, standard deviation and interval to find left-tail, right-tail and between-values probabilities.
normal bell curve
Project inputs
Normal Distribution Curve Calculator results
How this Normal Distribution Curve Calculator works
The tool standardizes each bound and evaluates the normal cumulative distribution using a numerical error-function approximation.
Important: Assumes a normal model; verify that assumption before interpreting probabilities.
What assumptions should I verify?
Check every entered quantity, unit, rate and rule against the current U.S. source that applies to your project. The calculator does not silently substitute worldwide conventions.
Is information sent anywhere?
No. Calculations run locally in the browser and the module contains no analytics, remote requests or stored personal data.